1. Field of the Invention
This invention relates to pipe swivel joints, and more particularly to pipe swivel joints especially adapted for use in constant motion service.
2. Description of the Prior Art
A production of oil and gas from offshore wells is a common endeavor in the petroleum industry. A well or cluster of several wells is drilled in the ocean floor and fluid from these wells transported by conduit to marine tankers which transport the fluid to shore facilities. A system of pipelines convey the fluid from the wells to a platform or floating buoy to which a marine tanker may be attached. The pipeline system includes one or more pipes or conduit extending generally horizontally across the ocean floor from the wells to a point below the floating buoy and a generally vertical pipe or hose extending from the buoy to the horizontal pipe. At a plurality of locations in the pipeline system connections are needed between the various pipes. A flexible hose or an articulated loading arm secured between the buoy and the marine tanker may include one or more connections. Some of these connections are used to permit one pipe or hose to rotate relative to an adjacent pipe or hose by the use of swivel joints. Some of the swivel joints include one joint portion which rotates relative to another joint portion on an occasional basis and other swivel joints include a first joint portion which is in almost constant motion relative to another joint portion. One location where a constant motion swivel joint is often used is in the flexible hose extending between the tanker and the buoy anchored to the ocean floor. In prior art swivel joints the seals of the joints wear rapidly due to the constant motion so the joint quite often fails and the seals must be replaced. When the joint is located beneath the surface of the ocean, especially at a great depth, such a replacement of seals is usually difficult and very expensive.
Analysis of the motion of the offshore swivel joints reveals a very large number of small oscillations of approximately 5 degrees or less, superimposed on a small number of large oscillations from 5-20 degrees and in addition, very infrequently a rotation of 360.degree. may occur. Since the majority of the oscillations are small in magnitude, it is seen that a swivel joint which isolates the seals and bearings of the joint from the small oscillations would greatly extend the useful life of such a swivel joint.